Protective device.



E. E. F. CREIGHTON.

PROTECTIVE DEVICE.

APPLICATION man MAY 2. 1912. RENEWED SEP1 .5. 1912.

1,261,71 1. Patented Apr. 2, 1918.

8-SHEET I.

2 SHEET Witnesses; Inventor":

.if almerEflFfCr-eighton, ja -m H W M hi qtporne E. E. F. CREIGHTON.

PROTECTIVE DEVICE.

APPLICATION FILED MAYZ, x912. RENEWED SEPT s. 1911.

1,261,71 1 Patented Apr. 2, 1918.

2 SHEETS-SHEET 2 Fig. 4. 9 Fig. 5

Witnesses: Inventor;

Crei "ton UNITED STATES PATENT oFFIoE.

ELMER E. F. CREIGHTON, OF SCI-IENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

PROTECTIVE DEVICE.

Application filed May 2, 1912, Serial No. 694,777.

To all whom it may concern:

Be it known that I, ELMER E. F. CREIGH- unit, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new, and useful Improvements in Protective Devices, of which the following is a specification.

My invention relates to protective devices for electric circuits, and more particularly to devices of that character which are adapted for use in circuits, such as the telephone, which comprise parts which can carryonly a small current. In order that such delicate apparatus be protected from the effects of high voltages however produced, whether by lightning or by the proximity of other circuits, it is necessary to provide means through which such abnormal voltages can discharge to ground before reaching the apparatus. At the same time, this means must be of such a nature that it will not allow the passage of current at the normal voltage of the system. Many devices of this kind in common use do not allow current to pass at the normal line voltage while in their original. condition but often allow it to pass at normal voltage after a very heavy abnormal current has once assed through them. This is due in art to using together of the metal parts an consequent decrease in resistance of the discharge path to ground.

The object of my invention is to produce a protective device of the above described character whichwill serve to protect the apparatus from the effect of an abnormal voltage and which at the same time will be as efficient in preventing the passage of current at the normal voltage after the passage of an abnormal current as before.

My invention contemplates the use of a series of blocks or electrodes of material which will roduce a discharge at-h of comparatively igh resistance. Pre erably I use metal blocks which are covered with a film of insulating material having a high resistance to discharge. Aluminum which is covered with a film of aluminum oxid is an Specification of Letters Patent.

Patented Apr. 2, 1918. Renewed September 5, 1917; Serial No. 189,885.

excellent material for this urpose because, as well l \:nown in the art, a umlnum oxid is a good insulator and adheres firmly to the metal. If the aluminum or' other metal blocks are placed in juxtaposition, the passage of the current rising from an abnormal voltage might cause the ends to fuse together and thus greatly diminish the resistance of the device. To obviate this difficulty, I alternate with the aluminum blocks other blocks of some refractory material, such as graphite. The several blocks are insulated from one another, preferably by being separated so as to form air gaps. This may be done b making the end surfaces of the said bloc rs irregular, or a separator composed of an insulating substance such as mica may be interposed between the same. The passage of current between a metal block and a graphite block will not cause the said blocks to fuse together since the arc will tend to burn away the graphite and increase the length of the gap. Moreover, by having a metal surface on only one side, there is much less chance of the fused metal bridging the gap. In order to insure that the alumlnum or other metal will oxidize and thus formv a film on the surface, it is desirable that an oxidizing agent be present in addition to that afforded-by the surrounding atmosphere. Manganese dioxid, or other-material which will give'ofi oxygen, may be filled into the spaces between the blocks of metal and graphite, or it may be incorporated in the graphite blocks.

Another means which I have devised for accomplishing the object hereinbefore setforth is to provide a pad composed of yielding refractory insulating material in which is embedded a plurality of metal filaments or fuses. Preferably such a pad is separated from the line electrode by an air gap.

The metal filaments may be of any easily fusible metal, such as zinc or lead, and may have a comparatively high electrical resistance. Upon the passage of current due to an abnormal. voltage, the metal filaments will fuse, thus interrupting their continuity,

increasing the resistance of the arrester, and stopping the flow of current. After the current has stopped flowin and the pad has cooled down, the meta filaments will be reformed owing to the condensation apparatus shown in Fig. 1; Fig. 3 is a section of a non-metal block; Fig. 4 is an elevation of another form of my invention; Fig. 5 is a vertical section of the same; Fig. 6 is a view showing the various parts of the pad forming part of my devlce; and Fig. 7 is a partial section of a modification of the device shown in Fig. 5.

In Fig. 1, a tube 1 of insulating material, preferably glass, is held in position on the switchboard or other suitable place by metal clamps or holders 2 fastened to the switchboard. A discharge path to ground through the tube 1 is formed by the blocks or electrodes 3 and 4 contained within the tube 1.

' The blocks 3 are preferably of some suitable metal, such as aluminum, which becomes coated with an insulating film when exposed to the air. Each block 3 is coated especially at the ends with a film of insulating oxid. The blocks 4 are of some non-metallic material, such as graphite, having fairly good conductivity and refractory enough to withstand heavy discharges. The block 3 at one end of the tube may be connected to the line and the block at the other end to the ground by means of suitable terminals or brackets 5, to which the end blocks are fastened by means of screws 6. The brackets 5 are provided with terminals 7 to which the leads may be attached.

The blocks 3 and 4 are suitably spaced in any convenient way to form a series of air gaps which will prevent current flow at normal line voltage but will permit abnormal voltage to discharge to ground. The graphite electrodes are interposed between the aluminum electrodes so that each spark gap has one electrode of aluminum and the other of graphite. As shown in Fig. 2, the gaps between the blocks 3 and 4 may be provided by means such as the corrugated separator 8, which may be of mica or other thin insulating material. The air gaps not only increase the discharge resistance of the device but also assure the formation of a film of oxid on the ends of the aluminum blo ks,

As shown in Fig. 3, the graphite block 4 may contain particles of manganese dioxid, which will also assist in oxidizing the aluminum as the discharge through the film to a particle of manganese dioxld will liberate oxygen by changing the particle into a lower oxid of manganese.

Two or more of the above described devices may be mounted in parallel on the switchboard and connected to a common ground with their other terminals connected to the line.

Upon the occurrence of an abnormal voltage sutficient to bridge the gaps between the several blocks, current will flow through the arrester to ground, whereupon the system is relieved of the abnormal voltage. Owing to the presence of the manganese dioxid or other oxygen producing substance, nascent oxygen w1ll be liberated and will assist in oxidizing the aluminum. The normal line voltage will not be able to cause current to follow the discharge of the abnormal voltage to ground by reason of the high resistance of the arrester due to the resistance of the blocks, of the film covering the aluminum blocks, and of the air gaps. The resistance of the arrester remains substantially constant during use, as the ends of the graphite blocks will tend to burn away to a small extent and thereby counterbalance any decrease in the air gap caused by projections or irregularities due to fusion of the surface of the metal blocks. The fact that no two metal blocks are adjacent to each other prevents the welding of one block to another.

The device shown in Figs. 4: to 6 comprises a base or block 9 of insulating material, such as slate or marble, provided with terminals 10 adapted to be connected with the line. Connected with these terminals are plates 11 which are connected by means of fuses 12 to plates 13 provided with terminals 14. Connected to one of the terminals 14 is conductive metal plate 15 which, as best shown in Fig. 6, has an offset projection 16 connected to said terminal. The plate 15 rests at the bottom of a depression in the insulating block as shown in Figs. 4 and 5. On top of the plate 15 is superimposed the separator plate 17, which may be of mica or other good electrical insulation andwhich is provided with cut-out portions 18. The pad 19 rests The plate 24 is provided with an Offset pro jection 25 by means of which it is connected to the other of the terminals 14. The block 26 of material similar to that of the block 9 is preferably placed over the plate 24. The block 26 and the intermediate parts are firmly held to the block9 by a bolt 27 with a nut 28. The terminal 29 which is connected to the plate 21 is also connected to the ground.

In operation, the terminals 10 are connected to the line, but owing to the resistance of the air gaps between the pads 19 and 22 and the plates 15 and 24, due to the separators 17 and 23, there will be no current passing from line to ground at normal voltage on the line. Upon an abnormal voltage being impressed upon the line in any way, the discharge caused thereby will bridge the gaps and arts through the pads by way of the metal filaments to the plate 21 and thence pass to ground. The discharge current will fuse the filaments, thereby greatly increasing the discharge resistance and preventing the line current from following the discharge to ground. When the device cools ofi, the metal filaments will substantially reform and the device will be again in condition for use.

When an abnormal current continues for any length of time, the fuses 12,'which are in series between the arrester and the line, should be blown. One way of securing'this result is shown in Fig.,7, which is a modification, wherein blocks 30 of carborundum or other material having a negative temperature coeificient of resistance are inserted at one end between the plates 21 and 15 and between 21 and 24 and are held in position by the separators l7 and 23. When an abnormal current passes through the arrester and the aforesaid blocks, their temperature will rise and their resistance will decrease. As shown in the drawing, the air gap between the carborundum blocks and the conducting plates 15 and 24 is smaller than that between the said plates and the pads 19 and 22. The result is that more and more current will pass through the carborundum blocks and the resistance of the circuit will rapidly decrease until the fuses 12 are blown owing to the corresponding increase in current. By this means the advantage of an arrester which will get rid of currents caused by high voltages which are imposed for a short time will be secured, and at the same time ,the arrester will be protected against a continued flow of such currents.

Various modifications of the device as shown in the drawings will suggest themath comprising a metal electrode with an msulating film thereon and a mass of me tallic oxid adjoining said film.

2. A protective device having a discharge path comprising a metal electrode and a cooperating electrode containing particles of metallic oxid capable of liberating oxygen through said mass.

5 A protective device comprising a plurality of aluminum electrodes and of raphite electrodes, a graphite electrode being interpcsed between each pair of alumlnum electrodes, and means for spacing all of said electrodes away from one another to form a plurality of spark gaps in series. I

6. A protective device comprising an insulating tube, a plurality of aluminum elec trodes extending through said tube, graphite electrodes interposed between said aluminum electrodes to separate each aluminum electrode from the next, and means for spacing said electrodes away from oneanother to form a plurality of spark gaps in series.

7 A protective device comprising a metallic electrode of a metal of which the oxid is an insulator, and a non-metallic refractory electrode mounted adjacent said metallic electrode and spaced away from said metallic electrode to form a spark gap between said electrodes.

8. A protective device comprising a metallic electrode on which an insulating film forms when said electrode is exposed to the air, and a non-metallic electrode spaced away from said metallic electrode to form a spark gap.

9. In a protective device, an electrode of a metal which becomes coated with an insulating film upon exposure to the air, a cooperating refractory non-metallic electrode, a spacer between said electrodes for positioning said electrodes with relation to each other, and means for holding said electrodes and said spacer in firm engagement. 1

10. A protective device having a discharge path comprising an electrode with an insulating film thereon, and a cooperating electrode adjoining said film and containing metallic oxid which is locally and ermanently converted into a lower oxid with liberation of oxygen by a discharge to said cooperating electrode.

11. A protective device having a discharge path comprising an electrode with a1 1 insulating film thereon, and metallic oxid 1n contact with said film and permanently changed locally by a discharge through said film to a lower oxid with llberation of oxygen at the point of discharge.

12. A protective device having a discharge path comprising an electrode with an insulating film thereon and particles of metallic oxid adj oinin said film and permanently changed by a dlscharge through said film into a lower oxid.

13. A protective device having a discharge path comprising an electrode with an insulating film thereon and manganese dioxid adjoining said film.

14. A protective device having a discharge path comprising an electrode with an insulating film thereon and a cooperating electrode having articles of manganese dioxid incorporated t erein adjacent said film.

In witness whereof, I have hereunto set my hand this 30th day of April, 1912.

ELMER E. F. CREIGHTON.

Witnesses:

BENJAMIN B. HULL, I'IEIEN ORFORD. 

